Radar and Navigational Aids



Radar is a device that uses radio waves to track distant objects. The main aim of radar is to determine:  whether there are objects in the region to be searched, the distance between the radar and the object, and the speed of the object as needed. Navigation aids are devices that assist vehicles to navigate in areas where signage is not available, such as at sea or in the air.

Radar- fundamentals

RADAR stands for RAdio Detection And Ranging. It consists of a transmitter and a receiver, both of which are linked to a directional antenna. The transmitter sends an Ultra High Frequency (UHF) or Microwave signal, while the receiver measures the echo signal returned from the target. When a pulsed signal is utilised in a transmitter, the distance between the transmitter and the target is estimated by calculating the time it takes for the signal to reach the receiver. If a continuous wave is utilised in the transmitter, the target's speed and direction of movement are estimated by detecting the signal frequency difference, which is known as the Doppler effect.

                                                       Figure 1.1: Basic Radar System 

Figure 1.1 shows a pulsed radar block diagram. It is made of a transmitter and a receiver, both of which are linked by a directional antenna. Through an antenna, the transmitter may send out UHF or big microwaves.

The receiver absorbs as much energy as possible from the target's echo, analyses the incoming signal, and displays it appropriately. The receiving antenna and the transmitting antenna are the same. Since radio energy is released in pulses, this is accomplished using a type of time-division multiplexing. The pulse is sent via the antenna. After some time, the echo signal or signal reflected by the object reaches the antenna. Because of the time delay, the time allocation approach is utilized to use the same antenna for transmission and reception.


·         The primary applications of radar include, but are not limited to, target search in open space or at sea, target tracking to follow target trajectory, and aircraft height readings.

·         Radar may be utilised as a navigation aid in a variety of ways. It has a wide range of military applications. Radar technology in aeroplanes can offer important navigational information. Radar equipment aboard ships gives information on land masses, other ships, and so on.

·         Radar is used in the military to deliver armaments to ships, planes, and direct missiles, among other things. Furthermore, radar is useful for aiding aeroplane landings, monitoring air traffic at airports, and allowing aircraft to fly above the ground.

Radar range equation

The reflected signal power that reaches the RADAR Receiver diminishes as the distance between the RADAR Transmitter and the target increases. The RADAR Receiver will be able to handle a certain amount of detectable power. The minimum power determines the greatest distance between the RADAR and the target, also known as the RADAR's Maximum Range. When the received power equals the receiver's lowest received power Pmin, the maximum range Rmax is reached. Rmax represents the maximum range. The equation of maximum range Rmax can be given as:

Where Pt = Peak value of the transmitted pulse power.

A0 = capture area of the receiving antenna.

S = Effective cross-section area of the Target (Also known as Radar cross-section)

Pmin = minimum received power

λ = wavelength of the transmitted signal

Factors influencing Maximum Range

The radar equation is given by

1. As per the above equation, the maximum range is proportional to the fourth root of the peak transmitted pulse power. To double the maximum range, the peak power must be raised 16 times while maintaining all other factors unchanged in the calculation. Such an increase in electricity is too costly.

2. A decrease in minimum receivable power has the same impact as increasing transmitting power and is thus a highly appealing alternative to it.

3. The radar range equation also demonstrates that the maximum range is proportional to the square root of the antenna's capture area, and hence exactly related to its diameter. To double a given maximum radar range, the effective width of the antenna must be doubled.

4. Increasing the frequency can also raise the Rmax. There is a limit to increasing frequency. An antenna's beamwidth is related to the wavelength/antenna diameter ratio. As a result, every increase in the diameter to wavelength ratio will result in a narrower beam.

Finally, the radar equation demonstrates that the maximum radar range is affected by the target area.

The basic pulsed radar system

A typical high power pulsed radar system is represented in Fig. 1.2. The modulator is supplied with rectangular voltage pulses by the trigger source. This voltage pulse is utilized as the output tube's supply voltage, switching it on and off. 

Microwave oscillators or amplifiers like klystrons, travel wave tubes, or cross-fields can be used in these tubes. The radar transmitter section is finished with a duplexer, which sends the output pulse to the antenna for transmission.

When no transmission is occurring, the receiver is linked to the antenna. A duplexer is used for this. In the receiver, the mixer is the initial step. It produces little noise. The primary receiver advantage is provided at frequencies of 30 or 60 MHz. The IF amplifier is tuned to the same frequency and has the same bandwidth characteristics as the RF amplifier. Finally, the detector is a Schottky blocking diode, the output of which is amplified by the same video amplifier as the IF amplifier. After that, the output is sent to the display unit. A cathode-ray tube is the most common type of display device.

Display methods

A radar receiver's output can be represented in various ways. The three most popular methods are as follows.

They are:

i) A scope

ii) Plan Position Indicator (PPI)

iii) Direct feeding to a computer

Separate displays may provide additional information such as height, speed, or velocity.

A Scope display

The display device works in the same way as a cathode ray oscilloscope. Sweep waveforms are employed on horizontal deflection plates of cathode ray tubes (CRTs). The beam steadily travels from left to right across the CRT screen before returning to its original place.

If no signal is received, the display in scope display A is a horizontal line. The demodulation receiver's output is sent to a vertical deflector plate, which causes the beam in the display to travel vertically, as seen in the figure. 1.3

The target distance is represented by the displacement from the CRT's left side. The initial 'blip' is created by a transmitted pulse. The other blip is a reflection from a nearby item, followed by a sound. Different targets then appear as big fixtures. The height of each beep correlates to the strength of the returned echo, while the distance from the reference bar is a measure of the distance.

Scope performance is great for tracking since only echoes coming from one direction are visible.

Plan Position Indicator (PPI)

• The timing wave of the sawtooth deflects the point of the cathode ray dramatically off-centre in this situation, therefore plan position indications are most often employed for this type of intensity modulation. It is timed with the sent pulse.

• The distance out from the centre of the display is proportionate to the target distance of the radar transmitter's echo production.

• The angular direction of the sawtooth beam location shows the orientation of the antenna beam.

The signal from the receiver output is applied to the control electrode of the cathode ray tube. The bias voltage at the control electrode is adjusted slightly higher than the cut-off voltage.

As a result, a signal with a high amplitude activates the spot. As a consequence, the target's echo shows as a bright spot with the target's distance and azimuth in polar coordinates. PPI screens are utilised in search radar and are especially useful when cone scanning is employed.

Automatic target detection

Manual radar performance might be inconsistent or incorrect. For example, the radar receiver's output is processed in a computer system before it is presented on the radar screen. Analogue computers can also be utilised to receive and analyse data, as well as for automated tracking and missile indications. A computer calculates the object's distance from the radar and speed based on the reflected signal and displays it on a monitor without the need for human interaction. These systems are referred to as automatic target detection systems since they function without human involvement.


Radar may be used to help navigation in a variety of ways. It has several military applications. Radar technology in aeroplanes can give valuable navigational information. Radar equipment aboard ships gives data on land masses, other ships, and so on.

Radar is used in the military to deliver weapons to ships, planes, and direct missiles, among other things. Furthermore, radar is useful for helping aircraft landings, monitoring air traffic at airports, and enabling aircraft height above the ground.

Aircraft landing systems

One of the most significant elements influencing the dependability of air travel is the ability to land an aircraft in poor or no visibility circumstances. Two electronic systems are typically utilised for aeroplane landing systems. They are:

(i) Instrument Landing System(ILS)

(ii) Ground Controlled Approach(GCA)

Both of these configurations are blind approach systems. The final landing is typically performed visually after the electronics system has brought the aircraft out of the overcast in the proper position to execute a landing.

Instrument Landing System (ILS)

Figure 1.4 shows the key components of the instrument landing system, which include a runway finding device, skateboard equipment, and a marking beacon.

Runway localization offers lateral guidance, allowing the aircraft to approach the runway in the proper direction. They are made up of a polarised bidirectionally polarised high-frequency radio network. A set of equations is derived using this radio network, as illustrated in the picture. 1.5. The track location's range differs from that of a long wave radio network.

                                                       Fig. 1.4. Instrument Landing System

The radiated wave in the runway localizer is composed of a single carrier wave. The carrier wave is concurrently amplitude modulated at 90 and 150 Hertz.

The two patterns in fig.1.5 correspond to the relative intensities of the 90 and 150 Hertz sidebands as a function of direction. The equi-signal course directions are therefore represented by equality in the intensities of the two modulations. In the receiver output, suitable filters separate the two modulated signals, which are then individually rectified and applied with opposite polarity to a zero-centre metre. As a result, metre deflection is absent when tone amplitudes are equal. If the tone intensity of the two signals differs, the stronger signal will deflect the pointer in a direction that indicates the direction in which the aircraft should fly to "correct" its flight.


Fig 1.5 Directional Pattern of Localizer and Glide Path in ILS.

Marker beacons are used to indicate position along the localizer route, as seen in fig.1.4. They are made up of low-power extremely high-frequency transmitters that excite antenna systems. This antenna arrangement generates fan-shaped beams. The beams are directed so that the wide dimension of the fan is perpendicular to the localizer route. Tone modulations and dot-and-dash keying are used to distinguish the various markers.

The glide-path equipment offers equi-signal path guidance in the vertical plane, comparable to the equi-signal path guidance in azimuth given by the localizer. The ideal gliding angle is between 2 and 5 degrees.

The glide path signal receiver isolates the two modulation tones, which are then rectified and applied to a zero-centre metre with opposite polarity.

This indicator is typically coupled with the localizer indication by housing the two-metre movements in a common casing in such a way that the localizer and glide-path pointers are vertical and horizontal when not deflected, respectively. Thus, any flight adjustments necessary to maintain the set courses in both the vertical and horizontal planes may be achieved with a fast glance at the one-meter face.

Ground Controlled Approach (GCA)

Two radars are used in the ground control approach system. The first is for general observation and to monitor aircraft traffic patterns around the landing strip. The second is a high-resolution short-range kit that is intended to practise landings. This second radar has two displays: one that shows elevation as a vertical displacement and rotates as a horizontal displacement, and the other that shows azimuth on the PPI indicator. The first display shows the matching glide path. The second display indicates the approach direction. The aircraft to be landed using this method is first brought into position using surveillance radar before beginning its descent. The controller on the high-resolution radar set indicator then takes over and occasionally informs the pilot on what needs to be done to ensure the aircraft is on the intended glide path. As a result, the aeroplane is "discussed" on a route that corresponds to the right landing, so that when the clouds breakthrough, it is in the correct position to visually complete the landing.

If the aircraft cannot be guided to the proper glide for whatever reason, it is commanded to abort the landing and return for a second attempt.

Advantage of GCA

The ground-controlled approach method has the benefit of requiring no equipment onboard the aircraft other than a standard radio receiver and allowing the ground installation to be transportable.

Dis-advantage of GCA

One of the drawbacks is that the network contains a lot of human links.

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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